Conventionally, navigation systems are used to search a route toward a travel destination and to provide a guidance of the searched route for a driver of a vehicle. In a navigation system, a position of the vehicle is detected and a map around the vehicle position is drawn on a display together with a vehicle position mark superposed thereon, and the map is scrolled on the screen for route guidance as the position of the vehicle is changed due to the travel of the vehicle.
Further, the navigation systems in recent years are equipped with communication functions to communicate with external servers and networks as well as reception functions to receive radio and TV broadcast and audio playback functions to play audio and/or video data on CD/DVD media or the like. Particularly, information of external events such as traffic congestions and/or accidents are available through the network, and update of map data for new roads and facilities are delivered from map distribution servers for an improved convenience of the user.
The communication functions are utilized for reception of weather information from the external sources, for displaying weather conditions and/or precipitation of a specific location based on the received weather information.
However, the navigation system described above is only capable of displaying the weather information acquired from the servers, and is not capable of presenting and drawing driver's attention to notices and warnings (typhoon information for example) in the traveling direction of the vehicle. Therefore, the driver of the vehicle has to check the weather notices and warnings after looking up the destination on the map when he/she uses the conventional navigation system.
A disclosure of Japanese Patent JP-A-2006-84250 describes a technique for displaying, for example, a weather forecast including a predicted course of a typhoon as inserted information on a display screen that is capable of displaying a roadmap when guidance points such as the travel destination and/or the current vehicle position are included in a typhoon influence area.
However, in the technique disclosed by above documents, a determination is made only to confirm whether or not the guidance points are included in the typhoon influence area. That is, in other words, the relation between the guidance route from the current position to the destination and a weather phenomenon such as a typhoon or the like is not taken into consideration. Therefore, the driver of the vehicle is still obliged to check the warnings after looking up the destination on the map even when he/she has the navigation system having the above guidance technique.
Further, the conventional navigation system is not capable of detecting the weather information in an actual condition even when the traffic information detection method for detecting the traffic information along the guidance route toward the destination is applied to the detection of the weather information due to the following reasons. That is, the traffic information regarding the traffic congestions, restriction on traffic lanes or the like is provided as an influence on the road, and the traffic information is determined as influential when the guidance route and the road under the influence of the traffic information is identical. On the other hand, the weather information such as rainstorm information should be considered as influential and should be reported for the driver of the vehicle even when the weather information being influential in a certain section in the grid of a weather information map is next to a section where the guidance route is passing, due to the nature of the weather information that cannot be clearly divided section to section in the grid map. However, the conventional traffic information detection method is not capable of suitably handling the weather information, that is, the conventional method cannot detect the influence of the weather information even in the next section of the grid map, thereby leading to an in-appropriate report of the weather information that does not reflect the actual condition of the reporting area.